Field of the Invention
The present invention relates to an optical scanning device suitable for an image forming apparatus, such as a laser beam printer and a multifunction printer.
Description of the Related Art
An example of a conventionally known optical scanning device for use in an image forming apparatus is the one that deflects a beam emitted from a light source using a deflector and guides the deflected beam to a scanned surface using an imaging optical system, to scan the scanned surface in a main scanning direction. Further, an example of a known scanning method of an optical scanning device is the one in which a printing area (an effective area) on a scanned surface is divided into two areas in a main scanning direction and the divided areas are scanned separately using two beams (a cascade scanning method).
Japanese Patent Application Laid-Open No. 2001-281580 discusses an image forming apparatus for scanning two printing areas on a common scanned surface in a separate manner using two optical scanning devices placed in parallel. Based on this configuration, an optical path length from a deflector to the scanned surface can be made shorter than an optical path length in a configuration in which a single optical scanning device scans the entire area of a printing area at the same scanning viewing angle. This configuration thus contributes to downsizing of the image forming apparatus.
In the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2001-281580, however, two optical scanning devices are provided. Thus, the number of components is large, and the entire apparatus is not sufficiently downsized. Further, with this configuration, if the position of the scanned surface is shifted in the optical axis directions, the incident positions (the printing positions) of two beams at the boundary between the two printing areas are greatly shifted in the main scanning direction. Thus, it becomes difficult to form an excellent image.